The project will attempt to elucidate the identity, three-dimensional relationship, and chemical properties of the groups which are responsible for the catalysis of conversion of delta-aminolevulinic acid to porphobilinogen by the enzyme delta-aminolevulinic acid dehydratase from bovine liver. The tools to be used are probes in the form of substrate analogs. Work will include inhibition by stereoisomers of substrate analogs and affinity labeling to identify active site residues. Since the enzyme appears to be a locus for the effects of lead poisoning, the effect of lead on certain steps of the reaction will be examined.